Generally, cooperative multi-point transmission (CoMP) may be considered in the Third Generation Partnership Project (3GPP) Long Term Evolution (LTE) Advanced as a tool to improve high data rate coverage, cell-edge throughput, and/or increase communications system throughput in both high and low communications system load scenarios.
In an uplink (UL) direction, where a User Equipment (UE), which is also commonly referred to as mobile station, subscriber, terminal, user, and so forth, transmits to an enhanced NodeB (eNB), which is also commonly referred to as NodeB, base station, communications controller, controller, and so on. UL coordinated multi-point reception implies reception of the UE's transmitted signals at multiple geographically separated points.
In a downlink (DL) direction, where the eNB transmits to the UE, DL coordinated multi-point transmission implies dynamic coordination among multiple geographically separated transmission points. An example of DL coordinated transmission schemes include coordinated beamforming where transmissions to a single UE is simultaneously transmitted from one of the transmission points and scheduling decisions are coordinated to control, e.g., interference generated in a set of coordinated cells.
Joint processing, which may include joint transmission (JT) and dynamic cell selection (DCS), is another example of a coordinated transmission scheme with more advanced interference mitigation capability. Joint transmission involves simultaneous transmissions to a single UE from multiple transmission points, e.g., to (coherently or non-coherently) improve the received signal quality and/or actively cancel interference from other UEs. DCS involves transmissions one source point at a time within CoMP cooperating set which is a set of one or more cells participating in CoMP operation with a UE.
DL coordinated multi-point transmission includes the possibility of coordination between different cells. From a radio-interface perspective, there may be no difference from the UE perspective if the cells belong to the same eNB or different eNBs. If inter-eNB coordination is supported, information needs to be signaled between eNBs, such as via an inter-eNB interface (e.g., an X2 interface).
Another form of coordinated transmission scheme is Multi-User (MU) Multiple Input, Multiple Output (MIMO), wherein transmissions to multiple UEs (or other destinations) sharing the same network resources (e.g., time domain and/or frequency domain network resources) may be differentiated in a spatial domain. A control channel is normally needed to schedule transmissions of each of the UEs participating in MU-MIMO. The UEs participating in MU-MIMO may be referred to herein as a UE pair or a UE group.
A heterogeneous network (HETNET) may be described as a communications system made up of high (transmission) power cells, such as macro cells, typically deployed as a planned network by a service provider, and low power node (LPN) cells, such as pico cells, femto cells, and so forth, that may be deployed by a service provider and/or a subscriber to help improve performance in high subscriber density areas or low coverage areas.